1. Field of the Invention
The present invention relates to a method for analyzing operation of a machine, and in particular, a method of reliability and constraint analysis for a machine.
2. Background Art
Recently, Factory Information Systems (FIS's) have become an important tool in automotive manufacturing. They can provide important information about the operation of various “assets”, such as robots, conveyor drives, weld guns, pumps, or other equipment used in manufacturing. A typical automotive FIS is based on a three layer information architecture, including a lower layer of asset controlling programmable logic controllers (PLC's), an intermediate layer of transfer PLC's, and a layer of servers that are accessible from an office automation (OA) network. Each of the asset controlling PLC's sends to a respective one of the transfer PLC's a standard package of data blocks. These data blocks can include, for example, data related to some or all of the following: cycle time, blocked time, starve time, downtime, fault vectors, and machine process parameters.
It is generally understood that cycle time includes the time during which a machine is performing its intended manufacturing operation, such as rotating, welding, stamping, spraying, etc., or it is in the process of preparing to do so—e.g., a portion of it is moving from one position to another, or it is changing tools. Conversely, a “blocked time” is a time during which the machine is forced to be idle because the next machine in the work cell or line is not ready to receive another part. A similar situation occurs when the prior machine in the work cell or line has not finished its operations, and therefore has no parts to transfer to the machine under analysis: in such a case, the machine is “starved”. “Downtime” can occur for any number of reasons, including tool breakage, machine failure, etc. As noted above, the data blocks can also include process parameters, which can include such information as standard cycle times, tool changes, number of operations, etc.
In the model discussed above, the transfer PLC's in one area may be linked in a virtual local area network (VLAN) with a gateway personal computer (PC) that isolates the lower layer of controlling PLC's from the OA net. The data for each area is organized in a database and stored on a server that is OA accessible. This architecture is the foundation of a web enabled FIS that allows for monitoring the operating attributes of the critical assets that are controlled or monitored by the PLC. A number of commercially available FIS's are commonly used in automotive manufacturing plants.
Despite providing some benefits over manual data collection, conventional FIS's are passive systems that produce predefined reports, and have limited analytical, modeling, and prognostic capability. These systems operate as a decision supporting tool, rather than a proactive algorithmic instrument that can autonomously implement and optimize some of the traditionally manual activities like evaluation of data integrity and feasibility, equipment reliability assessment, bottleneck constraint analysis, etc.
Therefore, a need exists for a method for automatically implementing at least some of these activities, for example, through an automatic reliability and constraint analysis agent that can be applied in a manufacturing environment to facilitate prediction of future machine operation.